1. Field of the Invention
The present invention relates to an adaptive optics apparatus and an imaging apparatus including the adaptive optics apparatus.
2. Description of the Related Art
Optical coherence tomography (OCT) using multi-wavelength optical interference is a method of acquiring a high resolution tomographic image of a subject (in particular, an eye ground). Hereinafter, an optical tomographic imaging apparatus that acquires an optical tomographic image by using OCT will be referred to as an OCT apparatus. In recent years, it has become possible to acquire a high-horizontal-resolution tomographic image of a retina by increasing the diameter of the measuring beam used in a Fourier domain OCT apparatus. On the other hand, the increased diameter of the beam diameter of the measuring beam has caused a problem in that, when acquiring a tomographic image of a retina, the signal to noise ratio and the resolution of the tomographic image is decreased due to the aberration generated by the distortion of a curved surface and unevenness of the index of refraction of a subject's eye. To address the problem, an adaptive optics OCT apparatus including an adaptive optics system has been developed. The adaptive optics system measures the aberration of a subject's eye using a wavefront sensor in real time and corrects the aberration using a wavefront correction device, so that a high-horizontal-resolution tomographic image can be acquired.
Japanese Patent Laid-Open No. 2007-14569 describes an ophthalmologic imaging apparatus including such an adaptive optics system. The apparatus is a scanning laser ophthalmoscope (SLO apparatus) that acquires an image of an eye ground by using an adaptive optics system, a liquid crystal spatial phase modulator, a polygon mirror, a galvano mirror, and other components. This ophthalmologic imaging apparatus corrects the aberration generated in a subject's eye by using the liquid crystal spatial phase modulator, thereby preventing the horizontal resolution from decreasing. In general, a liquid crystal spatial phase modulator modulates a specific polarization component aligned with the orientation of liquid crystal and does not modulate other polarization components. Therefore, it is difficult for the ophthalmologic imaging apparatus to correct a polarization component irrespective of the polarization state of reflected light reflected from the eye ground. In this respect, the ophthalmologic imaging apparatus has a room for improvement in acquiring a high-horizontal-resolution image. Regarding a spatial phase modulator for use in an adaptive optics system, “Progress report of USAF Research Laboratory liquid crystal AO program”, Proc. SPIE, Vol. 3353, 776 (1998) describes a transmissive liquid crystal spatial phase modulator in which two liquid crystal elements having different liquid-crystal orientations are stacked. This spatial phase modulator can modulate an incident beam irrespective of the polarization state of the incident beam.